As one of devices known in the technical field of this application, Patent Document 1, for example, discloses a device in which a liquid is discharged in a state of a liquid droplet from a discharge opening of a liquid chamber by quickly advancing a plunger toward the discharge opening and then abruptly stopping the plunger in the liquid chamber having the discharge opening.
In that type of known liquid material discharge device illustrated in FIG. 5, a piston is fixed to a rear end of a plunger such that the piston is biased forwards by a spring from the rear side. A part of a liquid material in a liquid chamber is discharged in a state of a liquid droplet from a discharge opening by supplying air to an inner space of a piston chamber forward of the piston so as to retract the piston together with the plunger, and then by releasing the air present forward of the piston to the atmosphere so as to advance the plunger. The plunger is stopped upon contacting with an inner wall of the liquid chamber, which is positioned forward of the plunger.
In the above known device, because the plunger advances in such a state that a circumferential surface of its forward end portion is held in non-contact with the inner wall of the liquid chamber, a part of the liquid material is allowed to move rearwards through a gap between the plunger and the liquid chamber. Therefore, resistance is small when the plunger is advanced, and the plunger can be smoothly advanced at a high speed.
Also, as a device differing in the principle of discharge, Patent Document 2, for example, discloses an applying device in which a liquid material is extruded by advancing a plunger which slides in a closely contact relation within a metering tube supplied with the liquid material. In such an applying device, the plunger is advanced by a piston rod which advances with the aid of an air piston chamber provided above the plunger and which strikes against an upper end of the plunger.    Patent Document 1: PCT Japanese Translation Patent Publication No. 2001-500962    Patent Document 2: Japanese Patent Laid-Open Publication No. 2004-225666